22 Artifact & Troubleshooting Practice Questions & Answers

Every Artifact & Troubleshooting practice question from the EKG Technician (CET) Practice Test, with the correct answer and a short explanation.

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1. A 12-lead tracing shows a thick, fuzzy baseline in every lead, made of a fine oscillation that is identical in height from wave to wave and perfectly regular in spacing, at about 60 cycles per second. The QRS complexes remain visible through it. Which cause best explains this appearance?
- A.Respiratory chest movement that tugs on electrodes applied to unprepared, oily skin
- B.A frayed wire inside the patient cable that makes and breaks contact while recording
- C.Skeletal muscle activity from a cold or anxious patient reaching the electrodes steadily
- D.Alternating current from nearby powered equipment coupling into the patient and wires✓ Answer
AC (60-cycle) interference is the only artifact whose oscillation is perfectly uniform in amplitude and perfectly regular in spacing, because it is driven by the 60 Hz line current of the building rather than by anything the patient does. Regularity is the discriminator: somatic tremor is jagged and irregular, and wandering baseline drifts slowly.
Source: NHA CET Test Plan (EKG Acquisition — causes and types of artifact: wandering baseline, somatic tremor, AC interference)Report a problem with this question
2. A tracing repeatedly shows uniform 60-cycle fuzz across all leads. The bed sits against a power strip and an infusion pump, and the patient's phone is charging on the sheet beside his arm. What should the technician do first?
- A.Move the phone and power cord away and straighten the lead wires along the limbs✓ Answer
- B.Switch on the 60 Hz notch filter first so the baseline smooths before recording again
- C.Lower the gain to 5 mm/mV so the interference looks smaller, then label the tracing
- D.Raise the paper speed to 50 mm/sec so the complexes spread out and the noise looks finer
AC interference is caused by an external electrical source, so the correcting action is to remove or move that source and keep lead wires straight and away from power cables. A filter, a gain change, or a speed change only alters how the noise looks on paper while the coupling continues.
Source: NHA CET Test Plan (methods to resolve artifact)Report a problem with this question
3. A tracing carries the uniform 60-cycle fuzz and the source of the interference has not yet been found. Why is engaging the 60 Hz notch filter treated as the last step rather than the first?
- A.It is a diagnostic setting that only a licensed provider is permitted to enable on a record
- B.It changes the effective paper speed, so every interval measured from the tracing is doubled
- C.It masks the noise on the printout without removing its source, and it can blunt the waveform✓ Answer
- D.It suppresses the standardization mark, so calibration can no longer be verified afterward
Filtering is cosmetic: the interference is still coupling into the patient and wires, and narrowing the recorded bandwidth can reduce amplitudes and blunt sharp deflections such as pacemaker spikes. Correct the physical cause, then use the filter only if noise persists.
Source: NHA CET Test Plan; AHA/ACC/HRS standardization recommendations on ECG filteringReport a problem with this question
4. Two noisy tracings are compared. On one, the baseline carries coarse, jagged deflections of varying height at irregular intervals; on the other it carries a fine oscillation of constant height at perfectly even intervals. Which statement assigns these two patterns correctly?
- A.Irregular, varying deflections are somatic tremor; the even, constant oscillation is AC interference✓ Answer
- B.Irregular, varying deflections are AC interference; the even, constant oscillation is somatic tremor
- C.Irregular, varying deflections are wandering baseline; the even, constant oscillation is a loose lead
- D.Irregular, varying deflections are a loose electrode; the even, constant oscillation is wandering baseline
Somatic tremor comes from skeletal muscle firing, which is never rhythmic, so its deflections vary in height and spacing. AC interference is driven by line current at a fixed 60 cycles per second, so it is uniform and evenly spaced; regularity separates the two.
Source: NHA CET Test Plan (wandering baseline, somatic tremor, AC interference)Report a problem with this question
5. A thin, elderly patient in a cold exam room is shivering visibly. All leads show coarse, spiky, irregular noise that buries the P waves, and the electrodes are fresh and firmly attached. What is the most appropriate first correction?
- A.Unplug the nearby infusion pump and move its power cord away from the bed
- B.Replace all ten electrodes with fresh ones and prep each site again with alcohol pads
- C.Cover the patient with a blanket and let him settle before the tracing is repeated✓ Answer
- D.Move the limb electrodes onto the torso so the shivering muscles are avoided
Shivering is skeletal muscle activity, and the electromyographic signal it produces is recorded as somatic tremor artifact. Removing the stimulus for shivering by warming the patient stops the muscle activity at its source, which no electrode change or machine setting can do.
Source: NHA CET Test Plan (somatic tremor: causes and resolution)Report a problem with this question
6. A patient with Parkinson disease has a continuous resting tremor of both hands. The six limb leads carry persistent coarse, irregular noise while the six chest leads are clean, and the patient cannot hold the hands still. Which measure is most appropriate?
- A.Record only the six chest leads and note on the tracing that the limb leads were unobtainable
- B.Ask the patient to hold both arms rigidly still for the ten seconds of the recording
- C.Move the limb electrodes proximally onto the upper arms and thighs, away from the tremor✓ Answer
- D.Engage the muscle filter and record the limb leads at half standardization instead
Moving a limb electrode toward the torso keeps the same limb but places the sensor on quieter, fleshy tissue farther from the tremoring muscle belly, which reduces the electromyographic signal reaching it. Any residual artifact that cannot be eliminated is then documented on the tracing.
Source: NHA CET Test Plan (electrode application in special populations; resolving somatic tremor)Report a problem with this question
7. On a 12-lead tracing the isoelectric line drifts slowly and smoothly up and down and the complexes ride along on the drift. The undulation rises and falls in time with the patient's breathing, and the QRS complexes themselves are sharp and undistorted. How should this be classified and handled?
- A.AC interference, addressed by moving the power cords and verifying the machine is grounded
- B.Somatic tremor, addressed by warming the patient and supporting both arms on the bed
- C.ST-segment elevation, addressed by reporting the tracing to the provider for interpretation
- D.Wandering baseline, addressed by re-prepping the sites and coaching quiet breathing✓ Answer
A slow, smooth undulation that follows respiration is wandering baseline, a contact and movement problem rather than an electrical or muscular one. It is corrected upstream at the skin and electrode interface and by quiet breathing, not by reporting it as an electrocardiographic finding.
Source: NHA CET Test Plan (wandering baseline)Report a problem with this question
8. Before a routine 12-lead, a patient applies scented body lotion to her arms and chest. During the recording the baseline drifts slowly in several leads and two electrodes are lifting at the edges. What explains the drift and how is it corrected?
- A.Lotion adds moisture that raises recorded voltage; lower the gain to 5 mm/mV and record again
- B.Lotion leaves an oily film that blocks conduction and adhesion; wipe with alcohol and re-electrode✓ Answer
- C.Lotion carries line current to the skin; move the power cord away and engage the notch filter
- D.Lotion cools the skin and provokes shivering; cover the patient with a blanket and record again
Oils and lotions raise skin impedance and stop the adhesive from holding, so the electrode moves and contact varies, which the machine records as a slowly drifting baseline. Cleaning with alcohol, allowing the skin to dry completely, and applying fresh electrodes restores a stable interface.
Source: NHA CET Test Plan (prepare the patient's skin)Report a problem with this question
9. A technician takes electrodes from a foil pouch that was opened four days earlier and left on the counter. The gel looks dull and feels tacky rather than moist. Several leads then show a drifting baseline with intermittent sharp spikes. What is the correct response?
- A.Moisten each dried electrode with a drop of saline and reapply it to the same prepared site
- B.Discard the dried electrodes and use fresh ones from a sealed pouch for the repeat✓ Answer
- C.Press each electrode down firmly for thirty seconds so the gel warms and contact improves
- D.Leave the electrodes in place and switch on the muscle filter so the spikes are smoothed
Conductive gel dries out once the pouch seal is broken, and a dried electrode gives high, unstable impedance that produces both drift and loose-contact spikes. Adding saline or pressing harder does not restore the manufactured gel, so fresh, in-date electrodes from a sealed pouch are required.
Source: NHA CET Test Plan (maintain supplies; causes and resolution of artifact)Report a problem with this question
10. The patient cable hangs over the side rail and pulls on the right arm and right leg wires. The baseline in several leads swings each time the patient shifts position, although the electrodes are new and the skin was prepped. Which correction addresses the cause?
- A.Record at 50 mm/sec so the drift is spread across a longer stretch of paper
- B.Tape each electrode down more firmly and leave the patient cable hanging over the rail
- C.Raise the gain to 20 mm/mV so the drifting complexes stay inside the channel
- D.Lay the cable on the bed so the wires hang slack without pulling on electrodes✓ Answer
Traction on a lead wire transmits every movement straight to the electrode and repeatedly changes the contact, which prints as a swinging baseline. Relieving the tension so the wires lie slack removes the mechanical cause; extra tape, a gain change, or a speed change leaves the pull in place.
Source: NHA CET Test Plan (cable care; resolving wandering baseline)Report a problem with this question
11. Coarse, irregular noise appears in leads I, II, and aVR. Leads III, aVL, aVF and all six chest leads are clean throughout the recording. Which electrode is the source of the problem?
- A.The right arm electrode, which contributes to leads I, II, and aVR✓ Answer
- B.The left arm electrode, which contributes to leads I, III, and aVL
- C.The left leg electrode, which contributes to leads II, III, and aVF
- D.The right leg electrode, which contributes to every lead on the tracing
Lead I is left arm minus right arm, lead II is left leg minus right arm, and aVR looks at the right arm, so the right arm is the single electrode common to exactly those three. Artifact confined to a group of leads always points to the electrode they share.
Source: NHA CET Test Plan (lead derivation and isolating the faulty electrode)Report a problem with this question
12. A tracing shows a flat, featureless line in lead III and low, distorted complexes in leads II and aVF, while leads I, aVL, aVR and V1 through V6 look normal. Which electrode should be checked first?
- A.The right arm electrode, since leads I, II, and aVR are all derived from it
- B.The left arm electrode, since leads I, III, and aVL all derive from it
- C.The left leg electrode, since leads II, III, and aVF all derive from it✓ Answer
- D.The V3 chest electrode, since the mid-precordial leads derive from it
Leads II, III, and aVF are the three that use the left leg electrode, so a failure there degrades exactly that group and spares the rest. The pattern of which leads are affected, not the appearance of the noise, is what localizes the faulty connection.
Source: NHA CET Test Plan (verify all leads recorded; isolate the faulty electrode)Report a problem with this question
13. Sharp, erratic spikes appear only in leads I, III, and aVL. Every other lead, including all six chest leads, records cleanly. What does this pattern indicate, and what should be done?
- A.The right arm electrode is the shared point; move the machine's power cord and record again
- B.The left arm electrode is the one point common to those leads; re-prep that site and replace it✓ Answer
- C.The whole patient cable is failing; replace the cable and record the tracing over again
- D.The patient is tremoring throughout; warm him with a blanket and record the tracing again
Leads I, III, and aVL are the three derivations that include the left arm, so an intermittent contact there produces spikes in exactly those leads. Because the fault is local to one site, the fix is local: re-prep the skin and put on a fresh electrode.
Source: NHA CET Test Plan (methods to resolve artifact)Report a problem with this question
14. Lead V3 shows a wavering, noisy baseline with intermittent dropout. Leads V1, V2, V4, V5, V6 and all six limb leads record cleanly from start to finish. What does this pattern localize the problem to?
- A.The chest cable as a whole, since the six chest wires pass through one connector
- B.The V3 electrode and its own wire, since no other lead shares that connection✓ Answer
- C.The left arm electrode, since the chest leads are referenced against that limb
- D.General patient movement, since tremor artifact appears in one lead at a time
Each precordial lead is recorded from its own single electrode, so a fault at V3 can affect only V3. If the connector or a global cause were responsible, neighbouring chest leads and the limb leads would be degraded as well.
Source: NHA CET Test Plan (precordial electrode application; isolating artifact by lead pattern)Report a problem with this question
15. Every lead of a 12-lead tracing carries the same fine oscillation at the same amplitude, and the noise does not change when the technician presses on any individual electrode or lifts any single wire. What does artifact affecting all leads equally point to?
- A.A single limb electrode that has dried out and is steadily losing contact with the skin
- B.One broken conductor inside the chest-lead portion of the patient cable
- C.Poor skin preparation at the V1 and V2 sites along the sternal borders
- D.A global source such as line current or an ungrounded machine, not one electrode✓ Answer
An electrode or wire fault can only degrade the leads that use it, so noise identical in all twelve leads and unchanged by manipulating individual sites must come from something shared by the whole recording, such as line current or a grounding fault.
Source: NHA CET Test Plan (AC interference; isolating global versus local causes)Report a problem with this question
16. Midway through a recording, lead V4 alone goes completely flat while every other lead continues to print normal complexes and the patient is alert and comfortable. What is the most likely cause and the correct response?
- A.The V4 electrode or its wire has come loose; check it and replace what has failed✓ Answer
- B.The patient is in asystole; stop recording and summon help to the bedside at once
- C.The machine has lost its ground; move the power plug to a different grounded outlet
- D.The gain has fallen to zero; reset the sensitivity to 10 mm/mV and record the tracing again
A true cardiac event would abolish complexes in every lead at once and would be accompanied by a change in the patient, so a flat line in one lead while the others are normal is a connection failure at that single site. The tracing is repeated only after all twelve leads record.
Source: NHA CET Test Plan (verify that all leads were recorded; replace defective clips and wires)Report a problem with this question
17. A patient with an involuntary tremor cannot stay still. After the room is warmed, the limbs supported and the sites re-prepped, a fine tremor artifact remains in the limb leads, although all complexes are measurable. How should the technician handle the tracing?
- A.Smooth the noisy segments by hand on the printout so the mounted tracing reads cleanly
- B.Trim the noisy portion and the standardization mark away before the tracing is mounted
- C.Record the best tracing obtainable and note that the artifact could not be cleared✓ Answer
- D.Record only the leads that came out clean and mount those six as the finished tracing
An electrocardiogram is a medical record, so altering, erasing or trimming it destroys evidence and is a records-integrity violation, and a partial tracing is not a completed study. When artifact cannot be removed at its source, the technician records the best obtainable tracing and documents the limitation.
Source: NHA CET Test Plan (mount the completed tracing; documentation and scope of practice)Report a problem with this question
18. A technician sees what looks like ST-segment elevation in V2 through V4, but the segment rises and falls with the slow undulation of the entire baseline and the apparent elevation changes from beat to beat. What should the technician do?
- A.Re-prep the sites, eliminate the drift, and repeat the tracing before anything is reported✓ Answer
- B.Report the tracing as showing anterior ST elevation and enter that finding in the record
- C.Raise the low-frequency filter setting until the ST segments print flat on the baseline
- D.Mount the tracing exactly as recorded and let the interpreting provider account for the drift
Wandering baseline displaces the whole waveform, so a segment that moves with the drift and varies beat to beat is a technical fault rather than a cardiac finding. The technician's job is to produce a technically adequate tracing, which means fixing the drift and repeating the recording rather than interpreting it.
Source: NHA CET Test Plan (scope of practice: the technician acquires but does not interpret)Report a problem with this question
19. A monitored patient's strip suddenly fills with chaotic, high-amplitude deflections. Which single feature on the strip itself most strongly supports artifact rather than a true ventricular arrhythmia, before the technician goes to assess the patient?
- A.Noise of greater amplitude in the chest leads than in the limb leads on the same strip
- B.Normal QRS complexes still marching through the chaos at the patient's previous regular R-R interval✓ Answer
- C.A measured rate above 150 per minute across the chaotic portion of the recorded strip
- D.Complete absence of any identifiable P waves throughout the chaotic portion of the strip
Artifact is added on top of the patient's own signal, so the underlying complexes continue at their previous regular interval underneath the noise, whereas a true ventricular arrhythmia replaces them. This finding still only raises suspicion: the technician must assess the patient and report a genuinely abnormal rhythm at once.
Source: NHA CET Test Plan (recognize cardiopulmonary compromise; report suspected life-threatening rhythms)Report a problem with this question
20. Complexes in V2 and V3 are so tall that they overlap the adjacent channels, so the technician reduces sensitivity to 5 mm/mV and records a readable tracing. What must accompany that change?
- A.The half-standardization must be marked on the tracing so amplitudes are not misread✓ Answer
- B.The paper speed must also be halved to 12.5 mm/sec so the proportions are preserved
- C.The 60 Hz notch filter must be engaged to compensate for the reduced sensitivity
- D.The tracing must be repeated at 10 mm/mV, since a reduced sensitivity is never permitted
Standard sensitivity is 10 mm/mV, so at 5 mm/mV every deflection prints at half its true height and voltage-based reading becomes wrong unless the reader knows. Labelling the tracing preserves the meaning of the millimetres printed on it.
Source: NHA CET Test Plan (verify EKG machine settings: speed, gain); standard calibration 10 mm/mV, 25 mm/secReport a problem with this question
21. Because the rate was very fast, a tracing is recorded at 50 mm/sec instead of the standard speed, and the change is never noted anywhere on the printout. What is the consequence for whoever reads that tracing later?
- A.Every complex prints at twice its true height, so the voltages will be read as too large
- B.Intervals are printed on a stretched scale, so the calculated rate comes out half the true rate✓ Answer
- C.The P waves are compressed into the QRS complexes, so the rhythm cannot be classified
- D.The standardization mark prints at half height, so the calibration cannot be verified
At the standard 25 mm/sec each small box is 0.04 second, and a reader assumes that scale. Doubling the speed doubles the width of every interval on paper, so an R-R interval measured as though it were standard yields a rate half the patient's true rate unless the speed is documented.
Source: NHA CET Test Plan (verify machine settings; label the mounted tracing); standard paper speed 25 mm/sec, 0.04 sec per small boxReport a problem with this question
22. A patient lies on a narrow table with both arms hanging unsupported off the sides and his head propped up on his elbows. The limb leads carry continuous coarse noise even though the electrodes are fresh and the skin was prepped. Which change prevents the artifact?
- A.Have him sit upright so the chest wall moves less while the tracing is taken
- B.Have him hold his breath for the whole ten seconds while the tracing records
- C.Have him grip the table edges firmly so his arms stay steady during recording
- D.Have him lie flat with both arms resting fully supported beside his body✓ Answer
Unsupported limbs and a propped posture keep the skeletal muscles contracted to hold the position, and that sustained muscle activity is recorded as somatic tremor artifact. Supporting the limbs lets the muscles relax, while gripping or bracing increases contraction and makes the noise worse.
Source: NHA CET Test Plan (position the patient; resolving somatic tremor)Report a problem with this question

Practice questions based on the NHA Certified EKG Technician (CET) test plan, the standard 12-lead electrode positions defined by anatomical landmark, and durable cardiac electrophysiology. CET is a mark of the National Healthcareer Association; this site is not affiliated with or endorsed by NHA. An EKG technician records tracings and does not diagnose. Always follow your facility's policies, your state's scope of practice, and the direction of the ordering provider. About the CET exam →

1. A 12-lead tracing shows a thick, fuzzy baseline in every lead, made of a fine oscillation that is identical in height from wave to wave and perfectly regular in spacing, at about 60 cycles per second. The QRS complexes remain visible through it. Which cause best explains this appearance?

2. A tracing repeatedly shows uniform 60-cycle fuzz across all leads. The bed sits against a power strip and an infusion pump, and the patient's phone is charging on the sheet beside his arm. What should the technician do first?

3. A tracing carries the uniform 60-cycle fuzz and the source of the interference has not yet been found. Why is engaging the 60 Hz notch filter treated as the last step rather than the first?

4. Two noisy tracings are compared. On one, the baseline carries coarse, jagged deflections of varying height at irregular intervals; on the other it carries a fine oscillation of constant height at perfectly even intervals. Which statement assigns these two patterns correctly?

5. A thin, elderly patient in a cold exam room is shivering visibly. All leads show coarse, spiky, irregular noise that buries the P waves, and the electrodes are fresh and firmly attached. What is the most appropriate first correction?

6. A patient with Parkinson disease has a continuous resting tremor of both hands. The six limb leads carry persistent coarse, irregular noise while the six chest leads are clean, and the patient cannot hold the hands still. Which measure is most appropriate?

7. On a 12-lead tracing the isoelectric line drifts slowly and smoothly up and down and the complexes ride along on the drift. The undulation rises and falls in time with the patient's breathing, and the QRS complexes themselves are sharp and undistorted. How should this be classified and handled?

8. Before a routine 12-lead, a patient applies scented body lotion to her arms and chest. During the recording the baseline drifts slowly in several leads and two electrodes are lifting at the edges. What explains the drift and how is it corrected?

9. A technician takes electrodes from a foil pouch that was opened four days earlier and left on the counter. The gel looks dull and feels tacky rather than moist. Several leads then show a drifting baseline with intermittent sharp spikes. What is the correct response?

10. The patient cable hangs over the side rail and pulls on the right arm and right leg wires. The baseline in several leads swings each time the patient shifts position, although the electrodes are new and the skin was prepped. Which correction addresses the cause?

11. Coarse, irregular noise appears in leads I, II, and aVR. Leads III, aVL, aVF and all six chest leads are clean throughout the recording. Which electrode is the source of the problem?

12. A tracing shows a flat, featureless line in lead III and low, distorted complexes in leads II and aVF, while leads I, aVL, aVR and V1 through V6 look normal. Which electrode should be checked first?

13. Sharp, erratic spikes appear only in leads I, III, and aVL. Every other lead, including all six chest leads, records cleanly. What does this pattern indicate, and what should be done?

14. Lead V3 shows a wavering, noisy baseline with intermittent dropout. Leads V1, V2, V4, V5, V6 and all six limb leads record cleanly from start to finish. What does this pattern localize the problem to?

15. Every lead of a 12-lead tracing carries the same fine oscillation at the same amplitude, and the noise does not change when the technician presses on any individual electrode or lifts any single wire. What does artifact affecting all leads equally point to?

16. Midway through a recording, lead V4 alone goes completely flat while every other lead continues to print normal complexes and the patient is alert and comfortable. What is the most likely cause and the correct response?

17. A patient with an involuntary tremor cannot stay still. After the room is warmed, the limbs supported and the sites re-prepped, a fine tremor artifact remains in the limb leads, although all complexes are measurable. How should the technician handle the tracing?

18. A technician sees what looks like ST-segment elevation in V2 through V4, but the segment rises and falls with the slow undulation of the entire baseline and the apparent elevation changes from beat to beat. What should the technician do?

19. A monitored patient's strip suddenly fills with chaotic, high-amplitude deflections. Which single feature on the strip itself most strongly supports artifact rather than a true ventricular arrhythmia, before the technician goes to assess the patient?

20. Complexes in V2 and V3 are so tall that they overlap the adjacent channels, so the technician reduces sensitivity to 5 mm/mV and records a readable tracing. What must accompany that change?

21. Because the rate was very fast, a tracing is recorded at 50 mm/sec instead of the standard speed, and the change is never noted anywhere on the printout. What is the consequence for whoever reads that tracing later?

22. A patient lies on a narrow table with both arms hanging unsupported off the sides and his head propped up on his elbows. The limb leads carry continuous coarse noise even though the electrodes are fresh and the skin was prepped. Which change prevents the artifact?